Crosslinking through transurethanization of cationic water-dilutable paint binders including for use in the formulation of cathodically depositable paints (CED-paints) is disclosed in the art. Among the first pertinent references making such disclosure are DE-OS Nos. 20 20 905, 22 52 536, 20 57 799, U.S. Pat. No. 3,799,854, and an article in Off. Digest, Feb. 1960, pp. 213-221. In the transurethanization, blocked or partially blocked polyisocyanate compounds are used. One of the main disadvantages of such systems is the high deblocking temperature which is necessary in application. Blocking agents with a low deblocking temperature, such as phenol, which are used in solvent-dissolved systems as described in U.S. Pat. No. 2,995,531, are not stable in an aqueous medium and thus cannot be used in the aqueous systems contemplated by the present invention. Other blocking agents having a low deblocking temperature, such as the N,N-dialkylglycolamides described in EP-Al-0 118 743, will sublimate in many instances and either remain in the paint films or lead to soilage of the stoving installations.
In an application filed in Austria, not yet published, diisocyanate compounds blocked with NH-functional enamines obtained at low temperatures from C-H-active dicarbonyl compounds and primary amines are disclosed. On deblocking, only low volatile decomposition products result.